1. Field of the Invention
This invention relates to the production of glass mats, and, more particularly, it is concerned with a glass fiber dispersion composition for making uniform, high-strength glass mats by the wet-laid process.
2. Description of the Prior Art
High strength, uniform, thin sheets or mats of glass fibers are finding increasing application in the building materials industry, as for example, in asphalt roofing shingles and as backing sheets for vinyl flooring. These glass fiber mats are replacing similar sheets made traditionally of asbestos fibers. Glass fiber mats usually are made commercially by a wet-laid process, which is carried out on modified paper making machinery, as described, for example, in the book by O. A. Battista, Synthetic Fibers in Papermaking (Wiley) N.Y. 1964. A number of U.S. patents also provide a rather complete description of the wet-laid process, including U.S. Pat. Nos. 2,906,660, 3,012,929, 3,021,255, 3,050,427, 3,103,461, 3,108,891, 3,228,825, 3,634,054, 3,749,638, 3,760,458, 3,766,003, 3,838,995, 3,905,067 and 4,052,257.
The wet-laid process comprises first forming an aqueous suspension or dispersion of a plurality of short-length glass fibers under agitation in a mixing tank. The fibers generally are available commercially as strands or bundles of many parallel fibers which filamentize or separate in the aqueous medium. The dispersion composition then is fed through a moving screen on which the fibers enmesh themselves while water is being removed.
Unlike natural fibers, such as cellulose or asbestos, however, glass fibers do not disperse well in water, even when stirred vigorously. In fact, upon extended agitation, the fibers actually agglomerate as large clumps which are very difficult to redisperse. In an attempt to overcome this inherent problem with glass fibers, it has been the practice in the industry to provide suspending aids for the glass fibers, including surfactants, in order to keep the fibers separated from one another in a relatively dispersed state. Such suspending aids usually are materials which increase the viscosity of the medium so that the fibers can suspend themselves without entangling. Some suspending aids actually are surfactants which function by reducing the surface attraction between the fibers. Unfortunately, however, none of the available suspending aids are entirely satisfactory for large volume manufacture of useful, uniform high strength glass fiber mats.
In the copending application, Ser. No. 851,683 (FDN-1062) filed Nov. 15, 1977, and assigned to the same assignee as the present application, there is described the use of amine oxide surfactants for forming well-dispersed glass fiber compositions. However, it is the object of this invention to provide improved dispersion compositions, which includes amine oxides in synergistic combination with another dispersing aid, for manufacture of uniform, high-strength glass mats suitable for industrial application.